The present invention relates to industrial two-layer fabrics excellent in rigidity, water drainage property, wear resistance, fiber supporting property and yield, and can be used for a long period of time.
Fabrics woven by warps and wefts have conventionally been used widely as an industrial fabric. They are, for example, used in various fields including papermaking wires, conveyor belts and filter cloths so that they are required to have fabric properties suited for the intended use or using environment. Particularly, papermaking fabrics used in a paper making step for removing water from raw materials by making use of the network of the fabric must satisfy a severe demand. There is therefore a demand for the development of fabrics which do not transfer a wire mark of the fabric to paper and therefore have excellent surface property, have dehydration property for sufficiently removing extra water contained in the raw materials, have enough rigidity and wear resistance and therefore are usable desirably even under severe environments, and are capable of maintaining conditions necessary for making good paper for a prolonged period of time. In addition, fiber supporting property, improvement in a papermaking yield, dimensional stability and running stability are demanded. In recent years, owing to the speed-up of a papermaking machine, requirements for papermaking fabrics become more severe.
Since most of the demands for industrial fabrics and solutions thereof can be understood if papermaking fabrics on which the most severe demand is imposed will be explained, the present invention will hereinafter be described by using the papermaking fabric as a typical example.
Papermaking raw materials are supplied on the upper side layer of a papermaking fabric so that the upper side layer is preferably dense and excellent in fiber supporting property and surface property. The lower side layer, on the other hand, becomes a surface with which a machine is brought into contact so that the lower side layer is preferably excellent in wear resistance, rigidity and water drainage property. It is said that an upper side layer has preferably a design in which a predetermined pattern is repeated regularly, but the design of a lower side layer is under investigation.
As a design of the lower side layer, various ones have been disclosed. For example, there is a ribbed fabric in which two adjacent lower surface side warps simultaneously pass over one lower surface side weft and under one lower surface side weft alternately as disclosed in Japanese Patent Laid-Open No. 2003-342889. The fabric having this design is excellent in water drainage property because a diagonal space is formed therein and in addition, it has an improved fiber supporting property on the surface because the shooting number of wefts can be increased. A crimp of lower surface side wefts which is brought into contact with a machine or roll is however short and does not protrude sufficiently so that a wear resistant volume of this fabric is small, which results in a problem of short lifetime.
A fabric developed to overcome the above-described problem is shown in Example 9 of FIG. 9 of US 2004/0079434. This fabric has improved wear resistance by forming a long crimp of lower surface side wefts in order to eliminate the above-described defect in the ribbed weave design. In this fabric, two adjacent warps have the same design as in the ribbed weave, but they have each a design in which a warp passes under one lower surface side weft and then passes over a plurality of lower surface side wefts adjacent to one another. The crimp of lower surface side wefts can therefore be made longer. However, this fabric also has a problem. Compared with the fabric of a ribbed weave design, this fabric has less weaving positions, which reduces its rigidity. In addition, wefts cannot be fixed firmly and undesirable movement occurs owing to a too long crimp of lower surface side wefts. As a result, the fabric does not have greatly improved lifetime in spite of an increase in the wear resistant volume of wefts.
A fabric having improved rigidity is shown in Example of US 2004/0182464. A lower surface side warp approaches lower surface side warps right adjacent and left adjacent thereto successively and is thus disposed in a zigzag manner so that the fabric has improved rigidity, but the undesirable movement of wefts cannot be prevented because of a too long crimp.
A fabric having a crimp of an adequate length while maintaining rigidity is considered. The fabric has, as shown in Conventional Example 1 and FIGS. 23 and 24 in this specification, a design of lower surface side wefts in which each passes over one lower surface side warp, passes under one lower surface side warp, passes over one lower surface side warp, and then passes under five successive lower surface side warps. When such a design is employed, the fabric has excellent rigidity because of an increase in weaving positions, is therefore firmly woven without undesirable movement of wefts, and has excellent wear resistance. Lower surface side warps of the fabric formed by shifting the design of the lower surface side weft by five warps each has a design in which it passes under one lower surface side weft, passes over one lower surface side weft, passes under one lower surface side weft and then passes over five successive lower surface side wefts so that the lower surface side weft over which the lower surface side warp passes is pushed to the reverse side of the fabric. As a result, wear of this portion precedes wear of the other portion. Owing to subsequent breakage, the fabric becomes unsuited for practical use. In short, although a fabric excellent in rigidity and free of undesirable movement of wefts can be obtained, wear resistance is not sufficient owing to partially uneven wear.
A papermaking fabric capable of satisfying such severe demands has not yet been developed.